1. Field of the Invention
The present invention relates to a method for the erasure of a static RAM and a corresponding integrated circuit memory.
2. Discussion of the Related Art
Static RAMs are used in many microprocessor-based applications, especially in data processing, to contain data elements on which computations or other processing operations are performed. RAMs are thus used to store data temporarily. When the power is turned off, they lose their contents, unless they have been associated with a back-up energy source (such as batteries or other energy cells).
Static RAMs are used in particular for smart card type products which are known to require a high level of security. These memories enable the application, in these products, of the different enciphering or other computations on confidential data elements stored therein.
It will be understood then that, to prevent any fraudulent use, it should not be possible to recover the data elements recorded in these static RAMs.
Now, even if these memories are "volatile", it cannot be certain that the data elements cannot be recovered when the power is turned off, for these data elements do not disappear instantaneously. There is a certain degree of remanence.
Thus, even if an anomaly is detected through various security sensors that may be planned and through associated security programs (such as voltage, frequency, temperature and passivation tests), the fact that the circuit has been turned off may not be enough to prevent the fraudulent recovery of sensitive data that has been stored in these memories.
Now, while it is possible for an external system to order the erasure of a static RAM by sending appropriate external control signals to the memory and by carrying out an address-by-address operation, this is a rather slow process, and resorting to security systems activated by external means is never satisfactory in terms of fraud control.